Merge in GO/dnsproxy from 331-upd-quic-go to master

Closes #331.

Squashed commit of the following:

commit df11453d
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Jun 5 19:10:10 2023 +0300

    all: imp docs

commit 8f27eb64
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Jun 5 18:55:58 2023 +0300

    proxyutil: rm depr

commit 4c72117e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Jun 5 18:49:06 2023 +0300

    upstream: fit into 100 cols

commit e67ff146
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Jun 5 17:29:49 2023 +0300

    all: upd dnsproxy